3D Positioning of a Ship Block at Hull Erection

Authors:Markku Manninen, Ilkka Kaisto

A.M.S. Ltd, Oulu/Finland

Practice Report

A.M.S.

3D Positioning of a Ship Block at Hull Erection

3D Building Frame System

Frame Point

Building Plane (BPl)

Building Axis (BA)

xy

z

3D Building Frame System (BFS) Axis Point

Parallel Axis Line to BPl

Principle Frame Point (PFP)

Object (OPl) Plane Object (OA) Axis

POP

OPl1

OPl2

Frame (FA) AxisOA1

OPl3/OA2

POP; Principle Object PointOPl1; First Object Plane PointOPl2; Second Object Plane PointOPl3; Third Object Plane PointOA1; First Object Axis PointOA2; Second Axis Point

Local Object References

Fig. 2. A simplified drawing of the 3D Building Frame System.

Fig.1. A simplified 3D wire frame drawing of a double bottom type of structure.The drawing is created using the DCP20 program of DCA-TC System

Fig. 3. A simplified drawing of a double bottom type of structure where thelocal object references are shown

IntroductionModern shipbuilders have widelyadopted the concept of modularconstruction and are realising the benefits associated with thesemethods [1]. The most criticalassembly phase is erecting thehull. It is most important that the huge 3D structural blocksassembled at this stage are accu-rately built. To achieve therequired manufacturing accuracythese structural modules arenowadays commonly built withexcess material which is trimmedbefore assembly. Advanced 3Dco-ordinate measurement tech-nology can be used to positionthese blocks efficiently at thehull erection site.

This application report describeshow the DAC-TC system is usedto establish a 3D Building FrameSystem at the site and how this frame system is used whenassembling the block structure.An example of such a structure is the double bottom of an eco-box type of carrier. A simplified3D drawing of such a block isshown in Fig. 1.

The DCA-TC SystemThe DCA-TC is a single sensor3-Dimensional Control andAnlysis System for shipbuildingand similar industries. Thesystem comprises Leica TC2002 a high

accuracy industrial 3D sensoras the measuring device

A.M.S. DCP10 a powerfulon-board dimensional controlprogram installed in a ruggedhandhold Control Unit andused for the dimensional controltasks at the production site,

A.M.S. DCP20 a dimensionalanalysis program run on a PCand used to present the resultsgraphically and numerically

3D Building Frame System(BFS) The 3D Building Frame System(BFS) is a 3D co-ordinate systemlocated at the erection site. It isthe reference system used todetermine the location of a pointin the building environmentduring the hull erection process.

A typical BFS is illustrated in aFig. 2. The BFS is established asdescribed below and the follow-ing terminology is used:

1. One plane is called theBuilding Plane (BPl). It isparallel to the plane definedby the x and y axis of theBFS. The orientation of theBPl is based on gravity or on some known (reference)points. Sometimes the planeis tilted with a known angleof inclination, which isdefined about the axis per-pendicular to the BuildingAxis.

2. One line is called theBuilding Axis (BA). This axisis parallel to the x axis of the BFS. The direction of theBA is determined by twospecific axis points. Oftenthe direction of the axis isclearly marked on the ground.Sometimes lines parallel tothe building axis are estab-lished and marked as well.

3. Permanent points are deter-mined and marked within theerection environment. Thesepoints are called FramePoints. The 3D co-ordinatevalues of the Frame Pointsare determined in the BFS.One frame point is definedas the Principle Frame Point(PFP).

Principle and local objectreferencesIn shipbuilding, a 3D co-ordinatesystem which is used as thereference system to determine thelocation of an object point iscalled the Ship Co-ordinate System(Ship CS). The entire ship geo-metry is determined using theShip CS as the reference system.

In shipbuilding the object align-ment (merging blocks together)is traditionally based upon the principle object references.These references are the BottomPlane (sometimes called BottomLine or BL), the Centre Plane(Centre Line or CL) and theFrame Plane (Frame Line or FrL).The reference planes appear as reference lines on the objectsurfaces. These principle objectreferences are organised in the Ship CS in the following way

The Bottom Plane is parallel tothe plane defined by the x andy axis of the Ship CS. The planedefines the zero value for the zco-ordinate.

The Centre Plane is parallel tothe plane defined by the x and z axis of the Ship CS. Theplane defines zero value for the y co-ordinate.

The Frame Plane is parallel tothe plane defined by the z and y axis of the Ship CS. Theorigin of the Ship CS definesthe zero value for the frameplanes.

In each object (structural moduleof the ship hull) we use thefollowing terminology for thelocal object references, whichare used for the alignment ofeach individual object (see Fig. 3for illustration):

1. One plane is called theObject Plane (OPl). Typi-cally the OPl is parallel to the Bottom Plane and isestablished with threeclearly defined plane points(OPl1, OPl2 and OPl3).

2. A primary reference line iscalled Object Axis (OA).Typically the OA is parallelto the Centre Line (CL) andis established with twoclearly defined object (axis)points (OA1 and OA2).

3. A line perpendicular to theObject Axis is called theFrame Axis (FA) and it can beestablished with two clearlydefined object (axis) points.

4. One object point is called thePrinciple Object Point (POP).

Positioning procedureThe positioning task is to align the first ship block on theerection site relative to theBuilding Frame System and thenthe following blocks relative tothe first block. (Fig. 4 illustratesthe positioning of the first block).The positioning task is carriedout with the aid of the DCP10program installed in the ruggedhand held Control Unit of theDCA-TC System. The Directionbased Orientation Method DOMis used to set-up the relationbetween the measuring instru-ment and the Building FrameSystem [5]. Here it is assumedthat the Building Plane of the

BFS is tilted with a known angleof inclination. The procedure of positioning a block on the hullerection site is as follows:

Step 1: Orientation of thesensor to the BFSFirst the horizontal plane of thesensor (active tilt compensator)is selected as the reference plane. Then the direction of theBuilding Axis (x direction of the BFS) is defined by measuringtwo axis points and then thePrinciple Frame Point (the 3Dco-ordinate values known in theBFS) is defined and measured as the point of translation. Finallythe Building Plane is rotated aro-und the y axis of the BFS withthe known angle of inclination.This completes the sensororientation to the BFS. Furthermeasured 3D co-ordinate valuesare then obtained in the BFS.(Note: The sensor cannot belocated on the deck of the blockwhile positioning.)

Frame Pointxy

z

3D Building Frame System

POP

Building Axis

Object Axis

Positioning a Block at Hull Erection

OPl1

OPl2OPl3

OPl4

OPl5

OA1

OA2

Object Plane

Principle Frame Point

Dimensional control on site with TC2002 and DCP10

Fig. 4. A simplified drawing showing the positioning of a double bottom type of block on the hull erection site usingthe Building Frame System as a reference

Illustrations, descriptions and technical data are not bindingand may be changed without notice.Printed in Switzerland Copyright by Leica AG, Heerbrugg, Switzerland, 1996

U1-299-0EN VII.96

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Step 2: Alignment of the ObjectPlane of the block with the Building Plane of the BFSFirst the block is approximatelylocated in its correct position and orientation. Then the ObjectPlane is aligned relative to theBuilding Plane. This is done by measuring the first plane point(OPl1) of the Object Plane and then two other plane points(OPl2, OPl3). The values areobtained in the BFS. The block is positioned so that the z co-ordinate of the two planepoints (OPl2, OPl3) are the sameas the z co-ordinate of the firstplane point (OPl1). (Some extra,redundant plane points, e. g.OPl4 and OPl5, can be used toensure there are no distortionsafter the block transfer.)

Step 3: Alignment of the ObjectAxis of the block with theBuilding Axis of the BFSThe first axis point (OA1) of theObject Axis and then the secondaxis point (OA2) are measured.The values are obtained in theBFS. The block is positioned sothat the y co-ordinate value of the second axis point (OA2) isthe same as the y co-ordinatevalue of the first axis point (OA1).Sometimes extra points can beused to guarantee the orientationof the block. If points OPl4 andOPl5 are used for that purposethen the x co-ordinate of thesepoints should be the same.

Step 4: Determination of the Frame Points in Ship Co-ordinate SystemAs a result of Steps 1-3 theObject Plane and the Object Axisare aligned with the BuildingPlane and with the Building Axisof the BFS respectively. Thismeans that the axis of the ShipCS and the axis of the BFS are parallel. The 3D co-ordinatevalue of the Principle ObjectPoint (POP) of the block definesthe position of the block in theShip CS. If the orientation of thesensor is done as described in the first step of this procedureand the Principle Object Point,POP (instead of the PrincipleFrame Point) is defined andmeasured as the point of trans-lation, then the 3D co-ordinatesof each measured point isobtained in the Ship CS.

After executing Steps 14 the 3Dco-ordinates of a selected set of frame points are measured andthe values are obtained in theShip CS. Subsequently the orien-tation of the sensor can each time be done directly in the ShipCS so that the next blocks arepositioned relative to the ShipCS. Regular checks are needed to maintain the orientation andthe position of the hull structurerelative to the BFS during theerection process.

Benefits of the 3Dpositioning When positioning block struc-tures at the erection site, 3Dmeasurements are required. Insuch cases 3D co-ordinatemeasurements based on the useof a single sensor are proven to be much more efficient andstraightforward than traditionalmeasurements [2], [3], [4]. The measuring accuracy of theTC2002 instrument is better thanone millimetre within a widerange (from 1.7 to hundreds ofmeters). This means that theDCA-TC system is well suitedfor positioning tasks erection ofthe hull. The high global accuracycan be maintained when thesame Building Frame System isused to position each individualhull module. It is also proventhat well defined alignment pro-cedures based on the 3D posi-tioning principle will lead to asignificant reduction in workinghours and in production time atthe hull erection stage [6].

References1. Yuuzaki, M., Okumato, Y.,

An Approach to New ShipProduction System Based onAdvanced Accuracy Control.Proceedings of the NSRP ShipProduction Symposium, NewOrleans, Louisiana, Sep. 1992.

2. Horsmon, A., Lupica C.,Advanced Industrial Measure-ment Systems for ProductiveShipbuilding. Proceedings of the NSRP Ship ProductionSymposium, Milwaukee,Wisconsin, Aug. 1990.

3. Manninen, M., Jaatinen J.,Productive Method and Systemto Control DimensionalUncertainties at Final Assem-bly Stages in Ship Production.Journal of Ship Production,Vol 8 Nov. 1990, pp. 244249.

4. Heikkil, R., Manninen, M.,Three Dimensional ControlSystem for Precast Architec-tural Concrete Production.Concrete Precasting Plant andTechnology, Iss. 10 (1994),pp. 6267.

5. Manninen, M., 3D Measure-ment and Analysis of a shipBlock. A.M.S. Publication No:6005 (Application report),Oulu Finland, 1996.

6. Schumacher, V., Verbal com-munication (Manninen/Schumacher). FlensburgerSchiffsbau-Gesellschaft, FSG,Flensburger, Germany, 1996.